Many passenger vehicles and light trucks are equipped with disc brakes and over time the surface of the brakes' rotors (where the brake pads engage the disc) will wear and decrease their effectiveness. Replacing the worn brakes/rotors is costly and time consuming. A cost effective alternative is to resurface the existing brake rotors. The brake lathe is designed to be attached to the lug bolts of a hub assembly of a passenger car or light truck that is equipped with disc brakes. The lathe includes cutting tips which are then capable of resurfacing the brake rotors while they are still attached to the vehicle.
Vehicle manufacturers require that certain standards be maintained on any resurfaced brake rotor. These standards regulate taper, parallelism, lateral run out (LRO) and rotor thickness. LRO is the total normal deviation from the theoretical plane which lies normal to the axis of rotation, as measured at a fixed radial position through one revolution of the surface. LRO is most commonly measured with a dial indicator. The indicator is placed at the outermost radius of the rotor face while the rotor is assembled on the vehicle. The hub/rotor assembly is then rotated and readings made on the indicator. LRO is the total displacement between the high and low readings.
Because of inaccuracies inherent to the hub assembly and the lathe mounting procedure, the central axis of the lathe is very rarely perfectly aligned with the hub's axis of rotation. Any angular misalignment between lathe and hub will cause the lathe cutting tips to move in a lateral motion while the lathe is in operation. This lateral motion can best be described as a sinusoidal movement of the cutting tips towards and away from the vehicle. Barring vehicle or lathe damage, this sinusoidal motion occurs with a period equal to one revolution of the hub/disc/lathe driveshaft assembly. Because the period is constant, this sinusoidal motion can be completely described by two factors: amplitude and phase. To compensate for the initial angular misalignment, and thus the LRO of the tips, an angular adjustment must be made. This adjustment must be equal in magnitude to the initial angular misalignment but it must be 180 degrees out of phase with the misalignment in order to bring the two axis into alignment. When the two axis are thus aligned, the LRO of the cutting tips has been minimized. Adjusting for this angular misalignment is known as LRO compensation.
Presently, LRO is compensated for with a system that requires the adjustment of three or more individual screws, which depending on the specific lathe/adapter combination being used, can be located at any point in the lathe/adapter/hub interface. To use this system, the lathe operator will first remove the wheel from the vehicle and then place an adapter over the lug bolts of the hub/brake assembly. Although there are various adapters for use with different vehicles, each adapter has a common face. The face of the adapter complements the geometry of the mounting face of the lathe's driveshaft. The center shaft of the lathe driveshaft is then screwed into the center of the adapter, bringing the lathe mounting face tightly against the adapter face. The indicator on the lathe is then employed to identify the degree of LRO that must be compensated for. The operator will then engage a combination of the adjustment screws to bring the central axis of the lathe into alignment with the hub's axis of rotation, thus compensating for LRO. There is no efficient way for the operator to pre-determine what combination of the adjustment screws will be necessary, and consequently, a great deal of time is spent engaging one, then another, then backing off on the previous one and so on, in an attempt to find the proper combination to overcome the LRO. This adjustment procedure is time consuming, especially tricky to train and ultimately requires an acquired "knack" to be performed efficiently.
Therefore, there exists a need for an easy to use, efficient and economical alignment device to be used with an on-vehicle disc brake lathe machine.